1. Field of the Invention
The present invention relates to shoulder replacement surgery. More particularly, the present invention the relates to implants that are used in shoulder arthroplasty. More particularly, the present invention the relates to a shock-absorbing element incorporated into such implants so as to avoid the risk of fracture and damage to either the surrounding bone and/or implant.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Every year, thousands of conventional total shoulder replacements are successfully carried out in the United States for patients with shoulder arthritis. This type of surgery, however, is not as beneficial for patients with large rotator cuff tears who have developed a complex type of shoulder arthritis called “cuff tear arthropathy”. For these patients, conventional total shoulder replacement may result in pain and limited motion, and reverse total shoulder replacement may be an option.
A conventional shoulder replacement device mimics the normal anatomy of the shoulder. In other words, a plastic cup is fitted into the shoulder socket (glenoid), and a metal ball is attached to the top of the humerus. In a reverse total shoulder replacement, the socket and metal ball are switched. The metal ball is fixed to the socket and the plastic cup is fixed to the upper end of the humerus.
A reverse total shoulder replacement works better for people with cuff tear arthropathy because it relies on different muscles to move the arm. In a healthy shoulder, the rotator cuff muscles help position and power the arm during the range of motion. A conventional replacement device also uses the rotator cuff muscles to function properly. In a patient with a large rotator cuff tear and cuff tear arthropathy, these muscles are no longer functional. The reverse total shoulder replacement relies on the deltoid muscle, instead of the rotator cuff, to power and position the arm.
Subsequent to the shoulder replacement surgery, the implant can be subjected to a large variety of forces. In particular, if a patient should fall, the implant may be subjected to extremely large impact forces. These impact forces have been known to fracture the ball which is attached to the glenoid. In other circumstances, the scapula can become fractured because of an impact. In other circumstances, the connection between the socket and the humerus can become loosened or detached. In still other circumstances, the humeral shaft can become fractured as a result of these forces.
Whenever these forces cause a damage to either the implant or to the bone structure, additional surgery may be necessary. Since the ball is attached to the glenoid, it becomes quite difficult to repair and replace the ball after installation. As a result, the implant can become loosened or nonfunctional. In particular, in shoulder replacement surgery, repairs to the implant, following the surgery, are quite complex. As such, a need has developed so as to provide a shoulder implant structure which avoids the damage that can occur from sharp impact forces imparted to the implant.
Shock-absorbing structures have been known to be used in hip replacement surgery. In particular, a variety of patents have issued relating to such shock-absorbing structures. In particular, U.S. Pat. No. 5,201,881, issued on Apr. 13, 1993 to D. L. Evans, shows a joint prosthesis that provides articulating prosthesis components that can deflect with respect to one another so that shock absorption is provided. This serves to lower impact stresses. The components interface at articulating surfaces. A gap is provided at a position away from the articulating surfaces. As a result, one of the components can flex into the gap area during use.
U.S. Pat. No. 5,389,107, issued on Feb. 14, 1995 to Nassar et al., provides a shock absorbent prosthetic hip implant that includes a socket section that is attachable to the pelvic bone and a ball section that is pivotably engaged with the socket section. There is a first shock absorber section attached to the ball section and a second shock absorber section attached to an upper part of the femur bone. The second shock absorber section slidably engages the first shock absorber section. A spring is disposed between the first and second shock absorber sections for cushioning a compressive force applied between the femur and pelvic bones.
U.S. Pat. No. 6,336,941, issued on Jan. 8, 2002 to Subba Rao et al., discloses a modular hip implant with a shock absorption system. The shock absorption system absorbs compressive stresses that are imparted to the implant. A unique coupling member houses a modular spring mechanism that serves as the shock absorber.
U.S. Pat. No. 8,070,823, issued on Dec. 6, 2011 to Kellar et al., teaches a prosthetic ball-and-socket joint. This ball-and-socket joint includes first member having a balanced centroidal axis and includes a rigid material with a concave interior defining a cup surface. The cup surface includes a cantilevered first flange defining a wear-resistant protruding first contact rim. The first flange is asymmetric relative to the balanced centroidal axis. A cantilevered second flange defines a wear-resistant protruding second contact rim. The second member is made of a rigid material with a wear-resistant convex contact surface. The first and second contact rims bear against the contact surface of the second member to transfer loads between the first and second members while allowing pivoting motion therebetween. The flanges are shaped and sized to deform elastically and permit the first and second contact rims to conform in an irregular shape to the contact surface when the joint is under load.
U.S. Patent Publication No. 2002/0143402, published on Oct. 3, 2002 to A. Steinberg, shows a hip joint prostheses that has at least a first and a second load-carrying member. The first load-carrying member is substantially more shock absorbing and resilient than the second load-carrying member.
U.S. Patent Publication No. 2006/0064169, published on Mar. 23, 2006 to B. A. Ferree, discloses shock-absorbing joint and spine replacements. In particular, the joint is a total knee replacement. This total knee replacement implant includes a femoral component having a wheel. The implant has a tibial component that includes a shock-absorbing component with a piston assembly and spring. The implants contain a cushioning or shock-absorbing member to dampen axial loads and other forces. Fluid is forced rapidly from the device wherein compression and dampening is achieved by valves or other pathways that allow for a slower return of the fluid back into the implant as the pressure is relieved.
It is quite natural that shock-absorbing systems have been utilized for knee and hip replacements since the knee and the hip are often subjected to large impact forces. However, typically, with shoulder replacements, the shoulders are not subjected to such strong forces, unless the patient should fall or be involved in an accident. As such, in the past, shock-absorbing systems for shoulder replacement implants have not been developed. As a result, under those circumstances where a patient should fall or be involved in an accident, extensive surgery can be necessary so as to repair the implant and/or the surrounding bone structures. As such, a need has developed so as to provide a shock-absorbing implant for shoulder replacement surgery.
U.S. Pat. No. 6,336,941, issued on Jan. 8, 2002 to Subba Rao et al., shows a modular implant with a shock absorption system. This is a modular implant that can be custom fit to an individual patient. The shock absorption system absorbs compressive stresses that are imparted to the implant. The size of the femoral ball member, size of the femoral stem, femoral neck length, and tension in the shock absorber system is available for all individually adjustable parameters, depending on the particular patient. A coupling member houses a modular spring mechanism that serves as the shock absorber. The coupling member is received into the ball member to an adjustable depth, the adjustment of which varies the length of the femoral neck.
U.S. Pat. No. 8,591,591, issued on Nov. 26, 2013 to Winslow et al., discloses a spring base glenosphere. In particular, this is a reverse modular humeral implant for implantation into a humerus that includes a natural humeral shaft and a natural humeral head. The implant includes a humeral stem implantable into the natural humeral shaft, and an adapter couplable to the humeral stem. The adapter includes an anchoring projection configured to be coupled to a convex bearing.
U.S. Pat. No. 5,080,673, issued on Jan. 14, 1992 to Burkhead et al., describes a glenoid prosthesis and method of use. The glenoid prosthesis has a lateral surface for articulating with the humeral head and a flat medial surface which engages a flat surface resected from the glenoid cavity. A pair of pegs extend medially from the flat medial surface of the glenoid prosthesis which are positioned in a pair of holes and the mating flat surfaces and pegs and holes are bonded with cement.
It is quite natural that shock-absorbing systems have been utilized for knee and hip replacements since the knee and the hip are often subjected to large impact forces. However, typically, with shoulder replacements, the shoulder prostheses are not subjected to such strong forces, unless the patient should fall or be involved in an accident. In the past, shock-absorbing systems for shoulder replacement implants have not been developed. As a result, under those circumstances where a patient should fall or be involved in an accident, extensive surgery can be necessary so as to repair the implant and/or the surrounding bone structures. As such, a need has developed so as to provide a shock-absorbing implant for shoulder replacement surgery.
It is an object of the present invention to provide a shock-absorbing implant which minimizes the transmission of forces to the glenoid portion of the implant or to the humeral head portion of the implant.
It is another object of the present invention to provide a shock-absorbing implant which mitigates micro-forces.
It is another object of the present invention to provide a shock-absorbing implant which creates a weak link such that an easily repairable portion of the implant will fail prior to a less easily repaired component of the implant.
It is still a further object of the present invention provide a shock-absorbing implant which avoids any fracturing of the bone and/or damage to the implant.
It is another object of the present invention to provide a shock-absorbing implant which is easily replaceable.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.